Process for the production of ethylene



ethylene.

United Par fO 2,972,647 rnocnss FOR THE raonucriost or ETHYLENE Kurt Fischeiy-Altotting, Upper-Bavaria, and Giinter Ruminert, Burghausen an der. Salzach, Germany, assignors to Farbwerke Hoevchst Aktiengesellsc haft vormals Meister Lucius & Briining, Frankfurt am Main Hochst, Germany, a company of Germany No Drawing. Filed May 24, 1954, Ser. No. 432,016 Claims priority, application Germany lune 1953 4 Claims. ci."2 0;sss

This invention relates to the production of ethylene and particularly to the production of ethylene inl high yield by. the thermal cracking of hydrocarbons wherein the by-products of the cracking process are re-cycled for further treatment to-produce additional quantities of It has,heretofor e, been known to produce benzines of low boiling point, as well as gaseous saturated and unsaturated hydrocarbons, by the cracking of heavy oils. In these processes, in order to obtain high yields-of *gas, it has been proposed to re-cycle unconverted oil and the liquid portions formed during thecracking stage for a V 3 second cracking, either under the sameconditions or under other conditions according to the desired purpose. The above described processes, which serve primarily for the production of benzine, generally seek to attain that condition. wherein the gaseous portion of the cracking products contains the greatest possible "proportion of the very valuable olefines' such as ethylene, propylene and 'butylene, besides the less valuable saturated hydrocarbons.

The olefines may be utilized in many types of chemical syntheses such as alkylations, oxo-synthesis, and the'like, ,1

while the parafilnes are, in part, subjected to a subsequent dehydrogenation. Until now, however, there have been no known processes in which heavy oil, re-cycled oil, gaseous saturated and unsaturated hydrocarbons, as Well as methane, in the presence of a portion of the hydrogen formed, are converted together in a single reaction and at the same temperature, so that ultimately only ethylene is formed as the principal product.

Although, when the individual gases are separately into the same reaction conditions, an optimum yield of the ethylene is obtained.

An example of the advantages of the simultaneous cracking of the combined components is illustrated by the fact that when butylene alone is treated at a temperature of 750 C., ethylene is produced; there are, however, also produced large portions of undesirable carbon and liquid hydrocarbons. Propylene, under the same conditions, produces very little ethylene. However, the combination of both of these-olefines, when cracked under the same conditions, results in a good conversion with .a high yield of ethylene. This is also true under the same conditionsnfor the. combination-of the total: portions of liquid and gaseous hydrocarbons formed. 1

Another advantage of the common cracking of liquid and gaseous hydrocarbons lies in the fact that, from the very'"beginning of the process, the speed of the flow is very high throughout the entire reaction zone. If the speed of flow is low, as in the case where liquid hydrocarbons are being cracked,'due to the fact that anincrease burn away the carbon deposits or a continuous replenishing and regeneration of the catalyst material. Although it has been, heretofore, attempted to prevent this carbon deposit by introducing certain inert gases together with the heavy oils, this is not necessary in the process embodied in this invention. 7

A further advantage of this invention lies in the fact that the lay-products of the cracking process, such as the aromatics and hydrogen, are continuously reintroduced into the reaction so that, within the framework of the carbon-hydrogen equilibrium, substantial new formation of these by-products no longer takes place. 5

The process of this invention requires only a minimum amount of apparatus, therefore, providing for good utilization of plant capacity while, at the same time, unusually high yields of ethylenes are obtained and only relatively small amounts of aromatic hydrocarbons, hydro- I gen and carbonare formed as by-products.

cracked, it is necessary to provide different conditions for the cracking of each gas in order to obtain high yields of ethylene, we have, surprisingly, found that if in addition to the constant replenishing with fresh heavy oil, the liquid and gaseous parafflns remaining from the prior cracking process are re-cycled through the cracking stage often enough, they will be almost completely converted to ethylene. In this re-cycling process, the methane is returned to the cracking stage where it, 'too, is converted to ethylene. Furthermore, a predetermined portion of'any hydrogen formed may be returned to the process in order' of the apparatusare-generally present whenever the cracking conditions are so chosenthab the conversion amounts 1 to atleast 50%. "We have found-thatithe optimum re- ""sults' are obtained-when-'the"reaction takes place "at temperatures of from about 500 C. to about 1100 C., and preferably at between about 700 C. to about 850 C.

It is the characteristic feature of our invention that if all the gaseous and liquid portions resulting from the cracking process of the oil are simultaneously introduced O'I" movable catalyst masses;

invention:

The most varied aliphatic or aliphatic-aromatic hydrocarbons and their mixtures, such as: diesel oil, kerosene, crude paraflin, etc. may be employed for the process. The process may be carried out in all of the suitable apparasmall chamber reactors and either wither Without fixed A's catalyst masses, there are suitable oxides of the second, third, fourth, and sixth 'grou'psof thepriodic' system, such as aluminum oxide, magnesium aluminum silicate, magnesium-aluminum molyb'clate and potassium-magnesium silicate. The introduction of heat may take place either through the walls of the reaction chamber or by the .useof. inert heat carriers. The alternating type of operation, according to the regenerator principle, may also be used.

The recovery of the .ethylene takes placeaccordingto any of the knownmethods by. absorption on active carbon or the like, by absorption in-solvents, by.the production of reversible chemical compo'unds, orfalso by. means of distillation. 1 1" The following are examples of processes illustrating the invention. However, these examples are merely illustrative .and are not intended to limit the scope 7 of the Ten kg. of a diesel oil (d.=0.84) were injected per hour into a coiled tube maintained at 750800 C. by external heat. There were mixed with this oil 16.5 kg. of a liquid hydrocarbon mixture (recycle oil) that had been produced from earlier charges. Simultaneously there were introduced at the same place 12.1 kg. of a gaseous hydrocarbon mixture consisting of the cracking gas from earlier charges, from which the ethylene and the hydrogen had been selectively removed and which possessed the following volumetric composition:

After one hour the following products were obtained:

16.4 kg. liquid hydrocarbons (re-cycle oil) 10.5 kg. propylene-l-butylene 5.9 kg. methane+ethane+propane+butane f 0.4 kg. hydrogen 4.2 kg. ethylene From the mixture of gases the ethylene and the hydrogen were separated selectively by adsorption on active carbon, and the entire remainder, together with the liquid hydrocarbons (re-cycle oil) obtained, plus kg. of fresh oil were returned into the reaction. This was done each hour.

At the end of 24 hours the following balance could be drawn up:

re-cycle gas 240.0 kg. fresh oil 100% produced. 161.9 kg. ethylene 67%. 10.2 kg. hydrogen 4.25%.

The remainder was completely used up, due to the formation of carbon and aromatics, whereby the carbon that was deposited in the reaction chamber must be considered as a loss. The amounts of re-cycle oil and recycle gas that were introduced together with the fresh oil at the beginning of the operating period were almost quantitatively recovered at the end.

Example 2 The operation was conducted exactly as in Example 1, except that instead of 12.1 kg. of hydrogen-free re-cycle gas, 12.9 kg. of re-cycle gas having the following composition were introduced:

The balance that was drawn after 24 hours gave the following yields:

240.0 kg. diesel oil 100% produced. 156.1 kg. ethylene 65.1%.

Remainder: Carbon and aromatics. The added re'cycle oil and re-cycle gas, introduced in the beginning, were recovered.

Example 3 In the same apparatus as in Example 1 there were injected in molten condition per hour:

10.0 kg. soft paraffin (M.I 30-40 C.)

5.5 kg. re-cycle oil from earlier charges 11.3 kg. re-cycle gas of the following composition (vo percent) Percent Butane V p 0.8 Propane 1.6 Ethane 3.1 Methane K 44.2 Butylene 16.9 Propylene 33.4

After one hour the following products were obtained:

4.5 kg. liquid hydrocarbon (re-cycle oil) 10.7 kg. propylene-l-butylene 4.9 kg. saturated hydrocarbons 0.5 kg. hydrogen 4.9 kg. ethylene re-cycle gas action tube. This was done every hour.

After 24 hours the following balance was drawn:

240 kg. paraffin produced. 179 kg. ethylene 74.6%. 17 kg. hydrogen 7.1%.

Remainder: Carbon and aromatics.

The re-cycle oil and recycle gas, introduced in the beginning, were quantitatively recovered.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. A process for the production of ethylene in high yield comprising the steps of thermally cracking hydrocarbons, having more than two carbon atoms, in a single reaction chamber to which fresh liquid hydrocarbons are continuously added, to form ethylene, carbon and byproducts, including methane, conducting the ethylene, carbon and by-products through separation stages for the removal of carbon and recovery of the ethylene, and then returning all hydrocarbon by-products to the single reaction chamber.

2. The process of claim 1 wherein the lay-products include hydrogen and wherein part of the hydrogen is separated out and part is returned to the reaction chamber with the remaining by-products, that part of the hydrogen which is returned being proportional to the amount of carbon that is separated during the same period.

3. The process of claim 1 wherein the cracking operation is made to take place at a temperature of between about 500 C. and about 1100 C.

4. The process of claim 1 wherein the cracking operation is made to take place at a temperature of between about 700 C. and about 85.0 C.

References Cited in the tile of this patent UNITED STATES PATENTS 2,498,806 Hachmuth "Feb. 28, 1950 2,597,346 Lefier May 20, 1952 2,621,216 White Dec. 9, 1952 2,653,903 Kilpatrick Sept. 29, 1953 

1. A PROCESS FOR THE PRODUCTION OF ETHYLENE IN HIGH YIELD COMPRISING THE STEPS OF THERMALLY CRACKING HYDROCARBONS, HAVING MORE THAN TWO CARBON ATOMS, IN A SINGLE REACTION CHAMBER TO WHICH FRESH LIQUID HYDROCARBONS ARE CONTINUOUSLY ADDED, TO FORM ETHYLENE, CARBON AND BYPRODUCTS, INCLUDING METHANE, CONDUCTING THE ETHYLENE, CARBON AND BY-PRODUCTS THROUGH SEPARATION STAGES FOR THE REMOVAL OF CARBON AND RECOVERY OF THE ETHYLENE, AND THEN RETURNING ALL HYDROCARBON BY-PRODUCTS TO THE SINGLE REACTION CHAMBER. 